To improve limitations of bandwidth capacity of optical fiber communication system in practical engineering applications, a photonic crystal fiber core structure which is capable of transmitting fundamental and high-order modes is proposed based on space division multiplexing technology. The effective refractive index curves of the corresponding modes under different structural parameters are obtained using the finite-difference imaginary-distance beam propagation method. An asymmetric dual-core photonic crystal fiber mode converter is designed by matching the effective refractive index curves of the two modes. It demonstrates that such an LP₀₁-to-LP₀₂ mode converter can be achieved at the wavelength of 1550 nm. In a wider frequency range, the mode coupling efficiency is above 90%, and the coupling length is about 178.5 μm. The device diameter is 47.6 μm, and the structural design is flexible and controllable, which can meet the needs of future large-capacity communication systems.